The invention relates to a seal for separating a first chamber from a second chamber in a device for aspirating and/or dispensing fluids, wherein the seal is embodied to be ring-shaped and to act on an outer surface of a piston, or an inner surface of a cylinder of this device, and wherein the seal can be inserted into an annular groove located in the outter surface of the piston, or the inner surface of the cylinder.
The invention further relates to a device for aspirating and/or despensing fluids. This device for aspirating and/or dispensing of fluids, having a first and second chamber, a seal for separating these two chambers and an annular groove for inserting this seal.
Automatic devices for aspirating and/or dispensing fluids in laboratories which, for example, are engaged in molecular-biological/biochemical testing, are known as automatic pipette devices, for example. O-ring seals for separating the cylinder (fluid and/or air chamber) from the exterior (atmosphere), whether fastened on the circumference of the piston or on the inner wall of the cylinder, are part of the prior art. One-way syringes, for example, for injecting medicaments, are known as the simplest form of a device for aspirating and/or dispensing fluids. With these syringes, O-rings, or also ring-shaped lip seals, which separate the rear (air) chamber from the front (fluid) chamber, are customarily partially inserted into a groove extending around the piston of the syringe. The same arrangement can also be found in automatic pipette devices with one or several xe2x80x9csyringesxe2x80x9d, which are essentially parallel with each other. However, often a seal is inserted into a groove cut into the inner surface of the cylinders, so that the pistons are moved, but the seals essentially remain stationary.
The friction between the seal and the piston, or between the seal and the cylinder, plays an increasingly important role in automatic pipette devices having a multitude of conduits (for example 8 or 96 conduits), for the parallel charging of the small pots or xe2x80x9cwellsxe2x80x9d in a micro-plate. In connection with the use of medical syringes it is known that the resistance caused by the friction at the seal surface is clearly perceived by the medical personnel. This friction can make the automatic functioning of a multi-pipette head, or multi-pipetting device, questionable. In contrast thereto, lip seals are known as low-friction seals.
The employment of so-called sealing mats for multi-pipette heads, or multi-pipetting devices, is also known. The precision achieved when punching out the holes in which the pistons of the multi-pipette head are later intended to move is so unsatisfactory in multi-pipette heads with, for example, 384 conduits, that it is not possible to sufficiently seal all 384 conduits, because it is often impossible to bring the position of the hole into satisfactory alignment with the position of the piston. Also, additional and expensive finishing of holes which became ragged in the course of punching is often required.
Since the movements of the sealing lip cause unacceptable changes in the cylinder volume, lip seals can make the reproducible reception and/or delivery of small volumes of fluids in the sub-milliliter, or in particular the sub-microliter range, more difficult, or impossible.
It is therefore an object of the present invention to propose an alternative seal, which at least partially eliminates the disadvantages found in the prior art.
It is a further object of the present invention to propose a device for aspirating and/or dispensing fluids, having a first and second chamber, an alternative seal for separating these two chambers and an annular groove for inserting this seal.
In respect to the seal, this object is attained by means of the characteristics of independent claim 1, in that a seal for separating a first chamber from a second chamber in a device for aspirating and/or dispensing fluids is proposed, which seal is embodied to be ring-shaped and to act on an outer surface of a piston, or an inner surface of a cylinder of this device, wherein the seal can be inserted into an annular groove located in the outer surface of the piston, or the inner surface of the cylinder. The seal in accordance with the invention is distinguished by comprising a flat contact surface embodied to rest against a flank of the annular groove, a support area freely projecting into the first or second chamber, and a cylindrical sealing face.
In respect to the device, this object is attained by means of the characteristics of independent claim 7, in that a device for aspirating and/or dispensing of fluids, having a first and second chamber, a seal for separating these two chambers and an annular groove for inserting this seal is proposed. The device in accordance with the invention is distinguished by comprising at least one seal in accordance with one of the claims 1 to 6.
Additional characteristics in accordance with the invention ensue from the dependent claims.
If a conventional seal (for example an O-ring) is used for sealing a chamber into which a piston can partially enter, and if this O-ring seals, for example, the outer circumference or outer surface of this piston, the following facts can be noticed: when the piston is moved, the seal is initially deformed until the adhesive friction between the seal and the piston has been overcome. This deformation of the seal causes a volume change in this chamber without the sealing face actually moving. The greater such a volume change is, the greater the resulting error during pipetting. If then the piston is moved over an extended distance, the sealing face can approach its desired position because of the low sliding friction between the seal and the piston and in this way practically compensate the volume error. However, pipetting in the sub-microliter range in particular demands the movement of the piston over very short displacement lengths, which causes the noticeable volume error and the concomitant poor pipetting precision.
Moreover, the volume error is a function of the state of the seal in respect to its mobility, elasticity, the portion of plasticizer in it and its erosion. This state changes over time, so that many different states can occur in multi-pipetting devices, in particular on account of the individual replacement of single seals. This state of the seal affects the friction between the seal and the piston. An undesired scattering of the precision of pipetting of the individual conduits results for all these reasons.
When using sealing mats in multi-pipetting devices it can occur that individual conduits, or perhaps even a single conduit, is not correctly sealed. In such cases it is necessary to exchange the entire sealing mat.
Therefore, among the advantages of the seal in accordance with the invention over the prior art are:
the cylindrical sealing face is supported on both sides in such a way that it is practically fixed in place in respect to the annular groove in which it is seated, and therefore can have no effect on the pipetting volume;
with short displacement lengths of the pipette piston the volume error is negligible;
pipetting in the sub-microliter range is independent of the state of the seal in respect to friction, mobility, elasticity, the portion of plasticizer in it and its erosion;
individual seals can be replaced at any time without the pipetting precision being impaired.
Preferred embodiments of the seal in accordance with the invention will be explained by means of the schematic drawings, without the latter restricting the scope of the invention.